Various exercise devices have been developed to strengthen an exerciser's musculature and improve his or her aerobic conditioning. Often these devices include left and right reciprocating members that are pivotally or slidably secured to a frame and reciprocated by the exerciser's legs, arms, or legs and arms. In particular, many devices have been developed including two reciprocating platforms or levers that are alternately depressed by an exerciser's legs to simulate stair climbing.
Conventional exercise apparatus with dual reciprocating members often include a linkage mechanism coupling the members together for completely dependent action. The linkage mechanism forces one member to move in the direction opposite of the other member during use. One such example is the exercise climber disclosed by U.S. Pat. No. 5,013,031 to Bull. Left and right reciprocating levers are connected by a rope and pulley system, such that when one lever is in the lowest position, the other lever is forced to the highest position, and vice-a-versa. Such conventional dependent systems act to impose synchronization on the exerciser's limbs, ensuring that each limb is exercised through the same range of motion and at the same speed.
The rigidity and inflexibility of such systems is not as appealing to some exercisers who may wish to exercise with a certain degree of unevenness. For instance, some exercisers may find it more natural to take greater or faster strides with one limb versus the other. To accommodate such action, other conventional exercisers have been developed that include independently operating first and second reciprocating members. One example is disclosed by U.S. Pat. No. 4,708,338 to Potts, which discloses a stair climbing exercise device including independently operating left and right levers. While enabling exercisers a greater degree of freedom in determining their strides, such independent action exercise devices may be undesirable for exercisers with less coordination or who wish to ensure that both of their limbs are subjected to the same degree of exercise.
It is thus desirable to provide an exercise device including a linkage mechanism that normally constrains the first and second reciprocating members to move in synchrony, while also enabling a limited degree of non-synchronous motion. One conventional manner for achieving this goal is embodied in a climber sold by Alpine Life Sports under the designation mark Tru-Climb 450.TM.. The Alpine climber includes a pulley mounted to the frame by a coil spring to enable the pulley to slide relative to the frame. Reciprocating step platforms are engaged with the pulley to enable non-synchronous motion. While such spring-mounted pulley climbers provide a more flexible system, the movable mounting of the pulley is somewhat complex, and therefore costly. Additionally, shear forces exerted on the pulley by the belt, when coupled with the loose tolerance required to enable the pulley to slide, may potentially result in undesirable wear of the system.
Thus, it is desired to construct an exercise apparatus wherein first and second reciprocating members are connected by a simple, reliable linkage permitting semi-dependent motion of the members. It is further desired to provide an exercise apparatus wherein the degree of non-synchronous motion of the first and second members is limited by the linkage so that, after a predetermined extent of non-synchronous motion has occurred, the first and second members are constrained to move in a dependent fashion.